Traditional light fixtures presently used in a typical office environment comprise a troffer with at least one fluorescent lamp and a lens having prismatic elements for distributing the light. Typical light fixtures may also use parabolic reflectors to provide a desired light distribution. The fluorescent lamp has long been the light source of choice among lighting designers in many commercial applications, particularly for indoor office lighting. A description of such a fluorescent light fixture may be found in U.S. Pat. No. 7,229,192, the contents of which is hereby incorporated by reference.
For many years the most common fluorescent lamps for use in indoor lighting have been the linear T5 (⅝ inch diameter), T8 (1 inch diameter), and the T12 (1½ inch diameter). Such bulbs are inefficient and have a relatively short lamp life. Thus, efforts have been made to identify suitable alternative illumination sources for indoor office lighting applications. Light emitting diodes (“LEDs”) have been identified as one alternative to traditional fluorescent bulbs.
An LED typically includes a diode mounted onto a die or chip, where the diode is surrounded by an encapsulant. The die is connected to a power source, which, in turn, transmits power to the diode. An LED used for lighting or illumination converts electrical energy to light in a manner that results in very little radiant energy outside the visible spectrum. LEDs are extremely efficient, and their efficiency is rapidly improving. For example, the lumen output obtained by 20 LEDs may soon be obtained by 10 LEDs.
However, in comparison to simply changing a light bulb in a conventional light fixture, exchanging an existing fluorescent fixture for a light fixture that uses LEDs as a light source can be labor intensive and costly. Such replacement typically requires access to the area above the ceiling. Environmental concerns, such as asbestos contamination and asbestos removal, become an issue when disturbing the ceiling. Moreover, the area above the ceiling collects dirt and dust, which can dislodge during LED replacement and thereby increase the time and cost of clean-up after installation. Additionally, exposed electrical wiring is common in such areas, which creates a safety hazard for workers removing old fixtures. A licensed electrician may be required to install the new fixtures based upon common safety codes. Thus, consumers are reticent to invest in a new LED light fixture when the effort and costs are compared to maintaining an existing fluorescent light fixture.
Efforts have also been made to retrofit an existing fluorescent light fixture with an LED light source. However, in an LED light source, the heat generated by the lamp may cause problems related to the basic function of the lamp and light fixture. Specifically, high operating temperatures degrade the performance of the LED lighting systems. Typical LED lighting systems have lifetimes approaching 50,000 hours at room temperature; however, the same LED lighting system has a lifetime of less than 7,000 hours when operated at close to 90° C. Thus, many retrofit LED light sources do not provide the anticipated benefits or longer life due to inadequate thermal dissipation. Therefore, there exists a need for an LED light source with adequate heat removal that can be retrofitted into an existing fluorescent light fixture.